Matrix and method of producing said matrix

ABSTRACT

The invention relates to a method of producing a matrix suitable for use in a plastic element-producing machine, a matrix produced in accordance with the method and the use of such a matrix to form a plastic element. One side of the matrix ( 2 ) is provided with a negative microstructure ( 2   a ) which is replicated in plastic material ( 3 ) to form a positive microstructure ( 3   a ) on a plastic element ( 3 ), wherewith the matrix ( 2 ) can be produced by applying a layer of material ( 7 ) to the positive microstructure side of a master. The positive microstructure side of the master has a thin wear-resistant layer ( 7 ) which serves as a first wear surface, wherewith said layer will present irregularities ( 7   a ) which correspond essentially to the microstructure, and wherein at least said irregularities are filled-in with a plastic composite ( 8 ′) so as to form a carrier element ( 8 ) for supporting the first wear layer ( 7 ). The layer ( 7 ) can further be provided with means for supplying heat energy to said matrix.

FIELD OF INVENTION

[0001] The present invention relates to a method of producing a matrixthat can be used in a compression moulding, embossing, injectionmoulding and/or other plastic element-producing machine. In particularlythe present invention relates to a matrix having a surface, or a part ofsaid surface, which is provided with a negative microstructure that canbe replicated as a positive microstructure, on a surface of a plasticelement, such as a compact disc (CD) formed in such a machine.

[0002] The invention also relates to a matrix manufactured by saidmethod, the use of said matrix to form a plastic element and the plasticelement so formed.

[0003] Definitions:

[0004] In the following, the expression “positive surface structure”shall be understood to mean the surface structure (including topographicsurface features such as microstructures or plane surfaces or parts ofsurfaces) that appears on a plastic element produced in a plasticelement-producing machine, and that by “negative surface structure” ismeant the inverse of the positive surface structure, i.e. the surfacestructure exhibited by a matrix used in such a machine.

[0005] By plastic composite is meant a curable mixture of polymericmaterial and a filling material, where the filler is normally present insurplus.

[0006] There is defined in the following description a matrix first wearsurface that is formed on a first wear layer, and a matrix second wearsurface that is formed on a second wear layer.

[0007] The first wear surface is the surface of the matrix that carriesa microstructure and that faces towards the manufactured plasticelement, while the second wear surface is the surface of the matrix,also referred to as the rear side, which is preferably planar and liesin abutment with the corresponding planar support surface of a mouldhalf. It will be understood that these latter two surfaces need notnecessarily be planar but that they shall connect with one another so asto be able to take-up forces generated during the moulding or castingprocess e g. they can have complementary shapes.

DESCRIPTION OF THE BACKGROUND ART

[0008] In respect of replicating microstructures on plastic elementsproduced in a machine of the kind defined in the introduction, it isknown to produce first an original master in some suitable way, and thento produce a matrix for use in said machine on the basis of this master.Matrices of this kind can be produced by coating a master or an originalthat has a positive microstructure on one surface with a metal layer ora metallic coating and removing the negative-microstructured metal layerfrom the master to thereby obtain a metal plate that can serve as amatrix in the compression moulding, embossing and/or injection mouldingpress Normally each mould half can have its own matrix and a flowing,hot (approximately 400° C.) plastic mass is pressed under high pressureinto a delimited mould cavity formed by cavities in brought togethermould halves The flowing hot plastic mass is then allowed to solidify(at approximately 140° C.) between the brought together mould halvesbefore the mould halves are opened and the solidified element can bepressed out.

[0009] Lithographic processes, in particular lithographic processes thathave been developed primarily for use in the micro-electrical field, arean example of known methods for producing a master. One of these methodsis based on etching a semiconductor surface and/or depositing materialthereon Other methods are based on the removal of parts of material withthe aid of a laser, so-called laser ablation, with the aid oftraditional NC-machines, with the aid of precision-controlled,high-speed diamond millers, with the aid of electric discharge machining(EDM), wire EDM and/or some other suitable method

[0010] Such originals or masters are normally produced from a materialthat is chosen to be suitable with respect to a given machining process

[0011] In the case of lithographic processes, the material is most oftena sheet of silicon, glass or quartz, whereas in the case of laserablation the material most often used is a sheet of plastic compositeand/or a polymeric material.

[0012] In the case of metal processing methods, plastics and soft metalsmay both be suitable

[0013] It is well known that the requirements of a given replicationprocess on a given material in the matrix and the plastic element arenot the same as the requirements that must be met with respect to theoriginal or the master. For instance, with respect to injection mouldingof such plastic elements where one or more surface parts shall present amicrostructure, one or both of the mould halves of the machine and thematrix used therein must be made of a stable material that can withstandthe high pressures that occur during the course of manufacture, andwhich will not be worn down unnecessarily quickly by the thermal andmechanical wear-and-tear to which the mould halves and the matrix aresubjected during the casting or moulding process.

[0014] It is known to produce such matrices, and primarily matrices foruse with microstructure, by transferring the shape and surface structureof a master to a metal plate which can then serve as a matrix

[0015] One manufacturing method is based on first producing a master ona surface of a glass plate, a semiconductor plate or a metal plate,coating the surface with a light-sensitive layer and exposing selectedsurface sections of this light-sensitive layer through the medium of alaser or the like, and washing and cleaning the selected surfacesections A metal layer is applied to the exposed and cleaned surface ofthe master, through the medium of a sputtering process, a vapourdeposition process, and/or through the medium of a plating or claddingprocess, for the length of time required to form a metal plate. Themetal plate can then be removed from the master. The metal plate has afirst surface which exhibits a negative microstructure which is intendedto face towards the inside of a mould cavity. The metal plate can beused as a matrix after further machining, i e smoothing, of a secondsurface that faces towards the mould half in the machine.

[0016] It is this method that is presently used in the manufacture of amatrix used in an injection moulding press for the production of opticaldiscs, e.g CD discs.

[0017] Other ways of producing a matrix or a master include:

[0018] an electrically insulating microstructured disc serving as amaster or matrix can be coated with a thin metal layer by means of asputtering process and/or by vapour deposition;

[0019] an electrically conductive microstructured disc or layer thatfunctions as a master or matrix can be coated with a much thicker metallayer by means of a plating or cladding process, a disc intended tofunction as a matrix can be coated with a thin electrically conductivelayer, such as a nickel, silver, or gold layer or some like metal layer,by means of a plating or cladding process.

[0020] It is also know to connect a metal layer electrically and tosubmerge a disc in a solution that comprises among other things, metalions, and to pass an electric current through the solution onto the discor master unit and therewith cause metal ions to precipitate as puremetal onto the surface of the disc. In this way a structure can beproduced in metal that has the inverse function of the microstructure onthe master.

[0021] It has been found that the above method can be readily applied inrespect of flatter structures, particularly when the depth of themicrostructure is limited to, or smaller than, about 0.2 μm

[0022] It has been found that in forming a matrix the metal build-up onthe microstructure-carrying surface of a master results in minor defectsor irregularities on the rear side of the matrix, which irregularitiesare caused by the microstructure, and that it is necessary tosubsequently smooth said rear side in order for it to lie in effectiveabutment, e.g. flat, on a flat surface on the mould half that supportsit in the pressing machine used.

[0023] Practical applications have shown that in the case of deeperstructures in the master microstructure, the master pattern will beembossed on the rear side of the matrix or metal plate.

[0024] Various procedures are known for reducing or eliminating thisproblem

[0025] A first measure is to apply an extremely thick layer of metal bymeans of a plating process or some equivalent process. The resultingplate which is intended to serve as the matrix will be strong andstable, The plate can then be placed in equipment in which the metallicrear side of the plate can be smoothed down or levelled mechanically,such as by a grinding, polishing and/or lapping process, while stillretaining sufficient strength to serve as a matrix

[0026] The process of applying a truly thick layer of metal as in thecase of deeper microstructures takes a relatively long time to achieve,for instance it will take from 10 to 20 hours to apply a nickel claddingwhich is a few millimetres thick.

[0027] Furthermore, it takes considerable time to grind and/or polishdown the metallic rear side to a smooth surface. Moreover, the adhesionbetween the master microstructure and the conductive metal layer in thematrix must be capable of withstanding the tensions that are generatedin the interface therebetween.

[0028] The use of available grinding and/or polishing equipment forsmoothing the metallic rear side to a flat surface also requires themaster to be very stable.

[0029] Various methods are known to counteract the problem arising froma defective or irregular and uneven rear side, by applying differentplating processes so as to be able to level out the growth of the metallayer against a planar metallic rear side.

[0030] One known method in this respect uses a pulsed field instead of adirect current with constant field. However, in principle, a metalliclayer takes longer to grow with a pulsed field than with a directcurrent. Using suitably adapted parameters and chemical compositions,this method enables the deep microstructure parts to be coated andbuilt-up more quickly than the shallower microstructure parts, meaningthat the deep structures will be overgrown and the metallic rear sidewill become relatively flat.

[0031] Practical experience has shown, however, that the metallic rearside must still be smoothed down, by grinding, polishing and/or lappingsaid surface.

[0032] With respect to the tine consumption of the two methods involvinga pulsed field and a constant field, the coating time in the firstmethod will be longer than the coating time in the latter method,whereas the time taken to smooth down said surface will be shorter inthe first method than in the second method.

[0033] When manufacturing plastic elements with a positive surfacerelated microstructure, different means and arrangements are known forsupplying the matrices belonging to the mould halves, and consequentlythe matrices in general, with alternating heating and cooling.

[0034] Heat is applied in order to thereby make the composite plastic orthe plastic material used more easily flowing against the surface of thematrix in order to in this way be able to improve the replicating of themicrostructure.

[0035] It is also known to apply cooling, such as a cold fluid, in theform of oil or water, or gas, in the form of air, to the mould halves ofthe matrix in order to thereby, immediately after the finishing of themanufacturing process in the machine, to, via the matrix, cool theplastic element down to the solidification temperature so that thepositive surface structure belonging to the plastic element remainsintact.

[0036] It is herewith obvious that because of the matrices' and themould halves' large heat storing capacity, large heat and coolingtransport system are required, which lead to a consequently slowmanufacturing speed.

[0037] Since the manufacturing speed is extremely dependent on the timetaken to heat up the matrix surface, by a heat supply to the mouldhalves, during the injection process and the time for a subsequentcooling of the cast element via the matrix surface and the mould halves,different measures have been suggested.

[0038] Thus, it has been suggested to form channels in the mould halvesand supply hot water respectively cold water through these, but becauseof the high pressure which exists inside the mould cavity it istechnically difficult to position them optimally close to the matrix.

[0039] With the intention of further reducing the cycle time it ispreviously known to use a heat insulating layer between the matrix andthe mould halves (see—Optimizing Pit Replication Through Managed HeatTransfer- by Thomas Hovatter, Matthew Niemeyer and James Gallo,published by GE Plastics, Pittsfield, Mass, USA).

SUMMARY OF THE PRESENT INVENTION

[0040] Technical Problems:

[0041] When taking into consideration the technical deliberations that aperson skilled in this particular art must make in order to provide asolution to one or more technical problems that he/she encounters, itwill be seen that on the one hand it is necessary initially to realisethe measures and/or the sequence of measures that must be undertaken tothis end, and on the other hand to realise which means is/are requiredin solving one or more of these problems On this basis, it will beevident that the technical problems listed below are highly relevant tothe development of the present invention.

[0042] When considering the present state of the art as described above,it will be evident that a technical problem resides in providing asimple method of producing a matrix that can be adapted for use in acompression moulding, embossing and/or injection moulding press, wherethe matrix is provided on one surface with a negative microstructurethat can be replicated in the machine as a positive microstructure on asurface part of a produced plastic element, through the medium of aplastic composite or plastic material, and therewith obtain aninexpensive matrix that has a sharply defined microstructure

[0043] Another technical problem is one of providing with the aid ofsimple means conditions that will enable the matrix to be given amicrostructure-related first wear-resistant surface formed on a firstwear-resistant layer which has an adaptable and relatively high abrasionresistance

[0044] Another technical problem is one of providing with the aid ofsimple means and measures conditions which will enable the matrix to bebuilt-up of at least two layers, a thin first wear-resistant layerpresenting said microstructure-related surface, and a layer whichstiffens or reinforces said thin wear-resistant layer, this latter layerbeing a thicker layer and which is referred to hereinafter as thecarrier element.

[0045] Still another technical problem is one of providing with simplemeasures conditions that will enable the material used in the first thinlayer and the material used in the thick layer or carrier element to bechosen with such properties and/or thicknesses as to fulfilpredetermined requirements and conditions.

[0046] Another technical problem is one of realising the significance ofand the advantages that are gained with enabling the matrix to beproduced by metal coating, with the aid of a metal coating process, amaster that has on one surface a positive microstructure, and coatingthis thin metal layer with a plastic composite so as to form saidcarrier element Another technical problem is one of producing withsimple means and measures a matrix which is formed substantially orexclusively from a plastic composite and which can be used in a machine,where the time taken to produce the matrix from a master has beenconsiderably shortened, among other things by being able to eliminate orat least substantially reduce the time taken to form on the plasticcomposite a flat rear side of the matrix for close abutment of said rearside with one of the two mould halves of said machine

[0047] Yet another technical problem resides in realising thesignificance of producing the matrix from a master and to apply to thesurface-carried positive microstructure a thin metal layer and to permitsaid metal layer to show on the rear side of the microstructureirregularities that correspond essentially to said microstructure, andto realise the advantages of filling said irregularities with asupportive plastic composite which, when cured forms a supportivesheet-like carrier element, instead of building up the entire matrixwith a thick metal layer

[0048] Another technical problem is one of realising the significance offilling-out said irregularities with a chosen plastic composite andforming the carrier element in a special mould cavity

[0049] Still another technical problem is one of realising thesignificance of and the advantages gained by, forming said plasticcomposite, and therewith said carrier element, from a mixture of plasticmaterial or polymeric material and a filler material such asquartz-filled or metal-filled epoxy or silicone polymer.

[0050] Another technical problem is one of realising the significanceof, and the advantages that are gained by, using a plastic composite andtherewith a carrier element that has a coefficient of linear expansionand/or a thermal conductivity and/or a heat capacity that is adapted fora given process carried out in the machine, and also to the design ofsaid machine.

[0051] In respect of this application, a technical problem resides inutilising a specially selected curing process so as to impart to thechosen plastic composite a hardness and/or hardening time which isdependent on the application concerned, by applying heat to chosen partsof the plastic composite or plastic mass and/or irradiating the plasticcomposite or said mass with UV-light, or by using a bicomponent plasticcomposite.

[0052] Still another technical problem is one of realising thesignificance of providing a first wear-resistant layer and/or a metallayer thin, and to select a plastic composite, and therewith a carrierelement, that has a low heat transfer capacity so that the plastic masspressed through the machine and between the mould part will be keptwarm.

[0053] Another technical problem is one of realising the significance ofand the advantages that are gained and the dimensioning rules requiredwith respect to the application of a second wear-resistant layer on thecarrier element surface distal from the microstructured surface of saidmetal layer.

[0054] Another technical problem is one of realising the significance offorming said second wear-resistant layer from a material that has lowfriction qualities against the flat surface of said mould half and highabrasive resistance, such as titanium nitride or diamond-like-carbon(DLC).

[0055] Still another technical problem is one of realising thesignificance of applying said thin metal layer to said master ororiginal when said original consists of an electrically non-conductivematerial, by means of a sputtering process and/or by means of vapourdeposition, and applying said thin metal layer by means of a metalplating process when said material is electrically conductive.

[0056] Another technical problem is one of choosing the thickness of themetal layer within predetermined limits on the basis of the applicationperformed in the injection moulding press

[0057] Still another technical problem is one of realising thesignificance of and the advantages that are to be gained by creatingconditions such as to greatly simplify smoothing-down of the rear sideof the matrix and of the carrier element and/or totally eliminating theneed of such smoothing.

[0058] There is a technical problem in, in a machine, for themanufacture of plastic elements, being able to form an arrangement whichwith the minimal possible application of energy shall be able to keepthe negative surface structure of the matrix hot during the mouldingprocess and thereby ensure a complete filling of the mould cavity beforethe plastic element is cooled.

[0059] There is furthermore the technical problem of how, with the helpof simple means and measures, the cycle time can be reduced for themanufacturing of an element in a machine of the type mentioned in theintroduction

[0060] There is also a technical problem within a machine for themanufacture of a plastic element, to be able to form an arrangementwhich with the smallest possible application of energy is able toquickly cool the negative outer structure of the matrix to a temperaturecorresponding with and somewhat under the solidification temperature forthe plastic mass

[0061] It is a technical problem to, with simple measures, be able toform such conditions within the matrix that a desired heating during themoulding sequence takes place inside the matrix and that the heatedmatrix serves as a barrier against a cold mould half and that a desiredcooling occurs only through simply disconnecting the heating sequence.

[0062] It should moreover be seen as a technical problem to be able toarrange conditions in order to achieve an electrically controlledheating of the negative surface structure of the matrix.

[0063] There is in this connection a further technical problem in atwith simple measures and with the use of one or more layers belonging tothe matrix being able to offer a simple and, if necessary, even locallyacting heating in order to in that way be able to increase thereplication capability.

[0064] It is moreover a technical problem to, via a matrix relatedarrangement, be able to form a locally acting intensive heating in orderto within the selected localities belonging to the mould cavity be ableto offer a better filling capability.

[0065] Then there is also a technical problem in for this purpose beingable to provide simple means and actions whereby an application ofelectrical heat energy to the whole of the matrix's surface structurecan be presented and furthermore, when necessary, a locally actingincreased application of electrical heat energy can be offered.

[0066] Then there is a technical problem in, with simple means, beingable to provide such conditions that said electrical heat energy shallbe able to be applied, via, or immediately beside, the negative surfacestructure belonging to the matrix, through applying a voltage to one andthe same layer for an adapted current distribution within said layerwhich can be conducting or semi-conducting

[0067] There is a technical problem in with simple measures being ableto form conditions for being able to offer a varying heat production,which only through selecting the thickness for a conducting orsemi-conducting layer with a thinner layer for a higher heat productionand vice versa.

[0068] Then there is a technical problem in with simple means being ableto form such conditions that said electrical heat energy and its localdistribution shall be able to be applied, via or immediately beside, thenegative surface structure belonging to the matrix through applying avoltage to two adjacent conducting layers for a current distributionwithin an intermediate semi-conducting layer.

[0069] It should be seen as a technical problem to with simple measuresbe able to form conditions for a varying heat production throughselecting thinner thickness and/or lower conductivity in delimitedsurface regions where a higher temperature is desired and vice versa.

[0070] There is also a technical problem in being able to realise thesignificance of and the advantages connected with using said layerhaving a negative surface structure and/or a layer supporting this layerwhen the latter consists of an electrically conducting or electricallysemi-conducting material.

[0071] There is also a technical problem in being able to realise thesignificance of selecting the layer having the negative surfacestructure belonging to the matrix from a material, normally a metalmaterial, with a resistivity of between 0.025 and 0.12 (ohm×sq mm/m).

[0072] There is also a technical problem in being able to realise thesignificance of and the advantages related to allowing the layer havingthe negative surface structure belonging to the matrix be supported by alayer with a resistivity of 0.03 and lower

[0073] There is also a technical problem in being able to realise thesignificance of and the advantages connected with allowing one or moresupporting layers to be made. of a heat producing layer such as anelectrically conducting polymer.

[0074] It should especially be seen to be a technical problem to be ableto realise the significance of the advantages related to that at leastone, of a plurality of available layers, is selected to have differentthicknesses, thicker at a section which requires lower heat energy andthinner at a section which requires higher heat energy.

[0075] The present invention specially relates to an application wherethe layer having the negative surface structure relating to the matrixis in the form of a microstructure and therewith being able to realisethe significance of allowing the heat production be adapted at selectedcross-sections to be higher than at other surface sections, in order toin this way similarly increase the replication accuracy and mouldfilling.

[0076] There is also a technical problem in being able to realise thesignificance of and the advantages related to allowing the heat energybe applied to a circular disk through applying a voltage between aperipheral surface part of a selected layer and a central hole.

[0077] Furthermore it should be considered to be a technical problem inbeing able to realise the significance of allowing the electrical heatenergy be applied to a circular disk through the application of voltageto a peripheral surface part for different layers with low resistivityand by heat production within an intermediate positioned layer with ahigh resistivity.

[0078] Solution

[0079] With the intention of solving one or more of the aforesaidtechnical problems, the present invention takes as its starting point amethod of producing a matrix that includes on one surface a negativemicrostructure which can be replicated in an injection moulding press asa positive microstructure on a prepared plastic element, from a plasticcomposite or a plastic material.

[0080] The invention is based on the concept of enabling said matrix tobe produced by covering a master or an original that has a positivemicrostructure on one side thereof with a layer of covering material.

[0081] It is now proposed in accordance with the invention that there isapplied to the positive microstructure on the surface of said master athin wear-resistant layer that functions as a first wear-resistantsurface, said layer presenting irregularities that correspondessentially to said microstructure, and then filling-out saidirregularities with a plastic composite, such as to form a carrierelement or backing element for said first wear-resistant layer.

[0082] By way of proposed embodiments that lie within the scope of theinventive method, it is proposed that said plastic composite is appliedto level out said irregularities in a mould cavity.

[0083] It is also proposed that the plastic composite, and therewith thecarrier element, is comprised of a polymeric material and a fillermaterial, such as quartz-filled or metal-filled or carbon fibre-filledor other fibre- or particle-filled epoxy polymer or silicone polymer

[0084] It is also proposed that the plastic composite, and therewith thecarrier element, have a coefficient of linear expansion and/or a thermalconductivity and/or a heat capacity adapted for a given process carriedout in a machine and also to the design of said machine

[0085] It is also proposed that the plastic composite is cured in amanner suitably adapted for injection moulding, such as by applying heatand/or irradiation with UV-light.

[0086] The plastic composite may also be a bicomponent composite.

[0087] It is also proposed in accordance with the invention that aplastic composite, therewith the carrier element, located beneath a hardwear-resistant layer serving as a first wear-resistant surface has anadapted thermal conductivity and/or an adapted heat capacity so that theplastic mass pressed forwards in the machine can be kept warn whileachieving short cycle times at the same time.

[0088] It is also proposed in accordance with the present invention thatthe plastic composite, and therewith the carrier element, can be coatedwith a second wear-resistant layer on the surface that lies distal fromthe first wear-resistant surface, so as to reinforce the matrixconstruction against abrasive wear.

[0089] This second wear-resistant layer may be comprised of titaniumnitrate or DLC

[0090] It is also proposed in accordance with the invention that saidthin first wear-resistant layer is comprised of a metal layer and thatsaid metal layer shall be applied by a sputtering process and/or avapour deposition process, or a metal plating process.

[0091] It is also proposed that the thickness of the firstwear-resistant layer, such as the metal layer, is carefully chosen withrespect to application and with respect to the design of the injectionmoulding press.

[0092] The invention also provides a matrix, which is adapted for use incompression moulding machine, an embossing machine and/or an injectionmoulding press.

[0093] It is particularly proposed in accordance with the invention thatthe microstructured surface of the matrix shall be comprised of a thin,first wear-resistant layer, such as a metal layer, and that said firstwear-resistant layer is preferably supported by a carrier element.

[0094] In accordance with proposed embodiments that lie within the scopeof the inventive concept, the carrier element is conveniently comprisedof a thick plastic composite layer.

[0095] In this regard, it is proposed that the carrier element becomprised of a plastic composite comprised of a polymeric material mixedwith a filler material, such as a quartz-filled or metal-filled or otherfibre- or particle-filled epoxy polymer or silicone polymer

[0096] It is also proposed that the carrier element will be comprised ofa plastic composite that has a coefficient of linear expansion and/or athermal conductivity and/or a heat capacity adapted to a chosen processand to a chosen design of the injection moulding press

[0097] It is particularly proposed that the carrier element is comprisedof a plastic composite that can be cured by applying heat and/orirradiating said composite with UV-light. Alternatively, the plasticcomposite may be a bicomponent composite.

[0098] The carrier element and the thick plastic composite layer mayalso be comprised of a plastic composite that has a pronounced lowthermal conductivity e.g. less than 2 W/m/° K.

[0099] It is particularly proposed that the carrier element can bestrengthened, primarily from an abrasion aspect, for instance with theaid of a second wear-resistant layer on the surface distal from themetal layer surface. This reinforcing second wear-resistant layer may becomprised of titanium nitride or DLC in this case.

[0100] It is further proposed that heating means be provided forsupplying heat energy to said matrix.

[0101] It is also proposed that said heating means should be formed bythe supplying of electrical heat energy to the whole, or parts, of justthe matrix, that said electrical heat energy is supplied via orimmediately beside the outer layer belonging to the matrix and that saidlayer and/or the supporting layer consist(s) of an electricallyconducting and/or electrically semi-conducting material.

[0102] As a suggested embodiment. falling within the scope of theinvented concept, it is taught that the layer belonging to the matrix isselected from a material with a resistivity of between 0.025 and 0.12Ohms×mm²/m.

[0103] It is further taught that said layer belonging to the matrix issupported by a further layer with a resistivity of 0.3 Ohms×mm²/m orless.

[0104] It is further suggested that such a supporting layer should beformed from a heat-producing layer.

[0105] The supporting layer can also consist of a material with a higherresistivity and positioned intermediate two layers having lowresistivity.

[0106] The invention further shows that such an intermediate positionedlayer can be selected to have different thicknesses, thicker at surfacesections that require low heat energy and thinner at surface sectionsthat require high heat energy.

[0107] The invention specially teaches the application of that the layerhaving the negative surface structure belonging to the matrix can havethe form of a microstructure and therewith requires that the heatproduction should be adapted so that it is greater at selected surfacesections than at other surface sections in order to thereby increase thereplication accuracy and mould filling.

[0108] The electrical heat energy can be supplied through applying avoltage to peripheral surface parts for a selected layer

[0109] Alternatively the electrical heat energy can be supplied throughapplying a voltage to peripheral surface parts of different layershaving low resistivity in order to produce heat within an intermediatepositioned layer having a high resistivity.

[0110] Advantages

[0111] Those advantages that are primarily afforded by a method ofproducing a matrix adapted for use in a compression moulding machineand/or an injection moulding press in accordance with the presentinvention reside in the creation of conditions which enable the matrixto be produced more simply. In particular, this can be achieved byapplying a thin first wear-resistant layer to the positivemicrostructure on one side of a master and thereafter applying a plasticcomposite in order to fill-out irregularities in said wear-resistantlayer and to form a carrier element

[0112] This eliminates, or at least substantially reduces, the need tosmooth down the plastic rear surface of the matrix in order to obtain aflat matrix surface which can abut a flat support surface of a mouldbody in the machine used.

[0113] The heat transfer capacity and/or the heat capacity of the matrixcan also be adapted so as to enhance the replication capacity in theproduction process, such as the embossment process and/or the injectionmoulding process, by virtue of the fact that the forming plasticmaterial will not freeze as soon as it comes into contact with themicrostructured surface of the matrix, but is able to remain fluid foras long as it takes to replicate the matrix microstructure effectivelyon the formed plastic element.

[0114] The matrix in accordance with the present invention, enables thethickness of an applied first wear-resistant layer, such as a metallayer, to be greatly reduced, thereby reducing the production time.Additionally, through the selection of a supportive plastic compositefor forming a carrier element, an adapted carrier surface can be formed,optionally with a wear-surface reinforcement, which can also function asa heat insulator and/or a heat storage between a hot pressed plasticmass and the matrix-associated mould part.

[0115] Further advantages such as being able to, with simple measures,offer a higher replication accuracy than previously and a more simplemould filling of an outer structure belonging to a plastic element, canbe obtained through supplying electrical heat energy to the whole orselected parts of the matrix.

[0116] The application of heat energy to the outer structure of thematrix occurs in the first place in order to be able to counteract oreliminate the matrix and mould half cooling effects on the heatedplastic mass, when it is squeezed in between the mould halves in themachine for the manufacturing of plastic elements.

[0117] Through the utilised and supplied electrical heat energy beingconcentrated to the outer layer of the matrix or in the vicinity thereofthe matrix and the mould halves can be given a temperature which isadapted for a quick cooling down of the plastic part by disconnectingthis supply of heat energy.

[0118] The primary characteristic features of an inventive method areset forth in the characterising clause of the accompanying claim 1,while the primary characteristic features of an inventive matrix are setforth in the characterising clause of the accompanying claim 13.

BRIEF DESCRIPTION OF THE DRAWINGS

[0119] The invention will now be described with reference to anembodiment of an injection moulding press at present preferred and inwhich an inventive matrix can be used, and with reference to a method ofproducing the matrix and to a matrix manufactured by said method thathas features significant of the present invention, with reference to theaccompanying drawings, in which:

[0120]FIG. 1 is a schematic side view of part of an injection mouldingpress and shows two mould halves in mutually co-operating positions;

[0121]FIG. 2 illustrates the machine of FIG. 1 in a stage of operationin which heated plastic mass in the form of a plastic composite is beingpressed through a fixed mould half and into a cavity formed between twomould halves, for pressure-casting or die casting of a flat plasticelement;

[0122]FIG. 3 illustrates the injection moulding press where a moveablemould half has been moved away from a fixed mould half and the shapedflat plastic element has been ejected from the moveable mould half;

[0123]FIG. 4 illustrates in perspective a microstructured matrix thatcan be placed in the moveable mould half, a simplified enlarged view ofpart of the microstructure also being shown in FIG. 4, although notaccording to scale;

[0124]FIG. 5 is a sectional side view illustrating one example of amethod of manufacturing a prior art matrix;

[0125]FIG. 6 is a sectional side view illustrating one example of amethod of manufacturing a matrix in accordance with the inventionmatrix;

[0126]FIG. 7 is a sectional view of part of a first embodiment of amatrix produced in accordance with the invention;

[0127]FIG. 8 is a sectional view of part of a second embodiment of amatrix in accordance with the invention, and

[0128]FIG. 9 illustrates the use of a mould cavity for producing amatrix that has a flat rear surface.

[0129]FIG. 10 shows in a perspective view the injection moulded planeplastic element, in the form of a CD-disk, at a distance outside themoveable mould half provided with a matrix,

[0130]FIG. 11 shows a cross-section a first embodiment of a negativesurface structure of a matrix,

[0131]FIG. 12 shows a cross-section of a second embodiment of a negativesurface structure of a matrix,

[0132]FIG. 13 shows a cross-section a third embodiment of a negativesurface structure of a matrix and

[0133]FIG. 14 shows a cross-section of a fourth embodiment of a negativesurface of a matrix.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED

[0134] The present invention relates to a method of producing a matrix2, in particular a matrix 2 adapted for use in a compression moulding,embossing, injection moulding and/or other plastic element-producingpress 1 One surface of the matrix 2 is given a negative microstructure 2a that can be replicated as a positive microstructure 3 a on a plasticelement 3 in the injection moulding press 1.

[0135] The method by means of which the matrix 2 is produced will bedescribed in more detail below with reference to FIG. 6.

[0136] For the sake of simplicity, the following description assumesthat solely the moveable mould half is provided with a matrix 2 that hasa microstructure 2 a, although the person skilled in this art willrealise that the fixed mould half may also be provided with such amatrix

[0137] Thus, FIGS. 1-3 illustrate schematically an injection mouldingpress I that includes an ejector rod 1 a, a number (3) of ejector pins 1b, a moveable mould 1 c and a fixed mould 1 d.

[0138] The moveable mould half 1 c and the fixed mould half 1 d definetherebetween a cavity 1 d whose shape conforms to the shape of a flat,injection moulded plastic element 3, said cavity including a cavityinlet If in the shape of an intake.

[0139]FIG. 1 also illustrates the use of a “pineapple” 1 g, a cylinderwall 1 h, a heating element 11, an injection ram 1 j and a fillingfunnel or hopper 1 k for granulated or powder material 1 m.

[0140]FIG. 2 shows how a heated, flowing plastic mass or plasticmaterial 1 p surrounds the “pineapple” 1 g and is pressed through thecavity inlet If by the plunger 1 g and into the cavity 1 e with themould halves 1 c, 1 d brought together in the position shown in FIG. 1.

[0141]FIG. 3 shows that the moveable mould half 1 c is moved away fromthe mould half 1 d to a given position in which the flat plastic element3 is parted from the moveable mould 1 c with the aid of the ejector rod1 a and the ejector pins 1 b, so as to fall out of the mould half 1 c.

[0142]FIG. 4 is a very simplified, perspective view of a plate-likematrix 2 which includes an upwardly facing microstructure 2 a on oneside thereof.

[0143] This microstructure is normally a very complex structure However,for the sake of ease of illustration of the present invention, anextremely simplified and enlarged embodiment of this microstructure isalso shown in FIG. 4, but not according to scale.

[0144] For the sake of simplicity and clarity, the following descriptionwill be concerned solely with a microstructure that includes a firstraised part 21, an intermediate cavity or hollow 22 and a second raisedpart 23.

[0145] The matrix 2 is thus provided with a negative microstructure 2 aon one surface thereof.

[0146] The matrix 2 has the form of a disc or a plate that has a flatundersurface 2 b, normally a flat machined surface 2 b, which rests on aflat supporting surface 1 c′ in the moveable mould half 1 c.

[0147] It is important in this respect that the matrix has a flat (orcurved) surface 2 b which is able to rest against a flat surface 1 c′(or a complementary curved surface) on the mould half 1 c, such that thematrix 2 will be able to withstand the pressure forces that aregenerated during the process of manufacture, for instance during aninjection press-moulding process.

[0148]FIG. 5 is a cross-sectional view of part of a known matrix 2,taken through the raised parts 21 and 23 and the cavity 22.

[0149] In the known method illustrated in FIG. 5, the matrix 2 can beproduced by coating a surface with metal through, for example, a metalplating process, to provide a master that has a positive microstructureon one side.

[0150] By means of this plating process, or corresponding process, metallayer upon metal layer are built up on the microstructure surface part 5a of the master, such that a first metal layer will cover even a lowestpoint in the microstructure on said surface part 5 a

[0151] Because such a plating process will result in a metal layer whoseupper surface will be irregular owing to the underlying surfacestructure 5 a, it is necessary to continue the plating process and formmetal layer up on metal layer until a combined thickness is reachedwhich will exceed, over the whole of said surface, a predetermined valueor plane, indicated by 6 in FIG. 5.

[0152] In the case of the earlier known method, it is necessary to grindaway all of the metal material 6 a applied over the surface 6, in oneway or another.

[0153] Plating processes for applying layers of the thickness concernedin this respect are very time-consuming. Grinding of the surplus metalmaterial 6 a down to the plane 6 is also very time-consuming.

[0154] According to the present invention, a matrix 2 is produced withthe aid of a master 5 that may be produced in the same way as the master5 shown in FIG. 5

[0155] According to the present invention, the surface-carried positivemicrostructure 5 a is covered with a thin wear-resistant first layer 7,shown in FIG. 6. This thin wear-resistant first layer 7 shall present anouter first wear-resistant surface 7 a. The expression “wear-resistantsurface” is intended to mean a surface against which the hot, flowingplastic material shall be pressed and against which the plastic element3 shall be formed prior to being removed from the mould halves 1 c, 1 d

[0156] The wear-resistant layer 7 that forms the first wear-resistantsurface 7 a will be sufficiently thin, for instance a thinness of 2 μm,for it to show a negative outer microstructure 2 a that correspondsexactly to the positive microstructure 5 a for the master 5.

[0157] The person skilled in this art is well aware of the fact that themethods and processes used in this regard will give different layerthicknesses and that it is necessary to choose a thickness and a methodwhich will ensure that the area between said raised parts will be keptopen.

[0158] The first wear-resistant layer 7 may be comprised of a plasticcomposite or some other hard material, although it is assumed in thefollowing description by way of illustration that this thin, firstwear-resistant layer 7 is comprised of metal.

[0159] The metal layer 7 can be applied with the aid of conventionaltechniques, for instance by sputtering or vapour deposition against anon-conductive master plate 5

[0160]FIG. 6 is intended to show that this thin metal layer 7 can beapplied to precisely cover the whole of the surface Sa allocated to themicrostructure with a thin layer of metal

[0161] In accordance with the requirements of the invention, the inneror upper surface of the thin metal layer 7 in FIG. 6 will presentirregularities 7 b that correspond substantially to the microstructure 5a

[0162] According to the invention, these irregularities 7 b are filledin a second stage with a selected plastic composite 8′. The plastic massused for this plastic composite 8′ should be hot and will besufficiently fluid to fill all cavities or hollows 22 and cover allraised parts 21, 23 and therewith provide a flat upper surface 8 a.

[0163]FIG. 6 is intended to illustrate an embodiment in which a plasticcomposite 8′ is applied to form a carrier element 8 in a manner suchthat a small proportion 8 a′ of the plastic composite will be locatedover the plane 6 and a contemplated flat surface 8 a, wherewith theexcess plastic material 8 a′ can now be easily removed by a mechanicalplanning process.

[0164] The matrix 2, in the form of a carrier element 8 and a thin firstwear-resistant surface 7 a, is lifted out of or away from the masterunit 5 and mounted in the moveable mould half 1 c with the surface 2 b(6) in abutment with the surface 1 c′.

[0165] According to the invention, the plastic composite 8′ that is usedto form a carrier element 8 may conveniently be applied under pressurein a mould cavity in a manner such as to obviate the need of machiningor mechanically working the rear side of the carrier element

[0166] This third stage in the manufacturing process will be describedin more detail below with reference to FIG. 9.

[0167] The use of a plastic composite 8′ and a carrier element 8 formedtherewith affords many adaptation possibilities It is well known thatdifferent polymeric materials and mixtures thereof admixed withdifferent fillers and mixtures thereof give different properties, andthat selected curing processes and curing times influence the finalproperties of the plastic composite. This knowledge offers manydifferent possibilities with respect to its application with a matrix inaccordance with the invention For instance, a plastic composite 8′ maybe chosen from a polymeric material that has been mixed with a fillingmaterial, such as quartz-filled, metal-filled or carbon-fibre or otherfibre or particle-filled epoxy or silicone polymers.

[0168] It is also proposed in accordance with the invention that theplastic composite 8′ and a carrier element 8 formed therefrom can bechosen to have a coefficient of linear expansion or a thermalconductivity and/or a heat capacity that is adapted to a chosen processand/or to the nature of the machine used.

[0169] The plastic composite 8′ may be chosen to cure in response toheat and/or through illumination with UV-light. These curingpossibilities may be conveniently utilised so as to enable the plasticcomposite to be adapted to give the requisite hardness and stiffness.

[0170] The plastic composite used may be a bicomponent type.

[0171]FIGS. 7 and 8 are intended to illustrate that when a plasticcomposite 8′ chosen to form a carrier element 8 located beneath the hardmetal layer 7 forming a first wear-resistant surface 7 a has an adaptedlow thermal conductivity (e.g under 2W/m/° K.) and/or an adapted highheat capacity (obtained by having a preferably high specific heatcapacity and/or a large mass), the plastic composite 8′ and the carrierelement 8 will function as a heat insulator against the mould half 1 c,so that the plastic material pressed forwards in the machine can be kepthot for the length of time taken for it to flow to and fill the mostdistant parts of the mould in order to form the microstructure pattern 3a in the plastic element 3.

[0172] In order to obtain an exact microstructure-related transfer, manyapplications require the heat and the temperature of the plasticmaterial pressed into the mould to be maintained in said materialwithout heat transferring to the mould half 1 c too quickly.

[0173] According to the present invention, the matrix 2, shown in FIGS.7 and 8, is coated with or has applied thereto a second wear-resistantlayer 9 that provides a second wear-resistant surface 9 a. This layer 9is applied to the surface 8 a of the carrier element 8 that faces awayfrom the metal layer 7 and may consist of a hard-wearing layer and/or aheat-insulating layer

[0174] The second wear-resistant layer 9 shall present to the surface 1c′ of the mould half 1 c a low-friction wear surface 9 a of highabrasive resistance, since the pressure between the matrix 2 and themould half 1 c is high during the casting or moulding process andthermal stresses tend to displace the matrix 2 relative to said mouldhalf 1 c.

[0175] The second wear surface 9 may, in this case, convenientlycomprise titanium nitride or diamond-like-carbon (DLC).

[0176] In certain applications, the material used to form the secondwear layer 9 may be the same material as that used to form the thin,first wear-resistant layer 7 a, with a plastic carrier element 8 placedtherebetween.

[0177] The thin metal layer 7 can be applied by a sputtering processand/or by vapour deposition, or by a plating or cladding process.

[0178]FIG. 8 illustrates an alternative embodiment which includes anabrasion-resistant second wear layer 9, a carrier element 8 formed by aplastic composite 8′ and a thin, first wear-resistant layer in the formof a metal layer 7, where a cavity or hollow 22 has the dimensions shownin FIG. 4, whereas an adjacent hollow or cavity 24 is much deeper thansaid cavity 22. A carrier element 8 having a carrier surface 8 b for thethin first wear-resistant layer 7 and/or said layer 7 may comprise aplastic composite 8′ having a coefficient of linear expansion and/or athermal conductivity and/or a heat capacity adapted to a chosen processand/or to the design of the moulding machine used. Preferably thecoefficient of linear expansion is lower than 1×10⁻⁵/° K. so that themoulded structure does not change shape too much when exposed to theextremes of temperature found in plastic element manufacturingprocesses.

[0179] The carrier element 8 may also be comprised of a plasticcomposite that can be given different degrees of hardness, by applyingdifferent degrees of heat and/or by irradiation with UV-light

[0180] The carrier element 8 may also be comprised of a material thathas a low thermal conductivity and a high heat-insulating and/or heatcapacity in order to prevent it absorbing too much heat energy from thehot plastic mass.

[0181] The carrier element 8 may also be reinforced with known means.For instance, the carrier element 8 may be strengthened with a furtheranti-wear layer 9 on the surface thereof that lies distal from themetalled surface 7.

[0182] Although the invention has been described above with reference toan embodiment in which a thin wear-resistant layer 7 is supported by athicker plastic layer or carrier element 8, it is suitable in certaincases to form these two wear-resistant layers from one and the sameplastic material.

[0183] There is nothing to prevent the wear-resistant layer 7 fromcuring first, preferably to a high degree of hardness, and curing thesupportive plastic layer or carrier element 8 at a later time to a lowerdegree of hardness.

[0184] As illustrated in FIG. 9, the plastic composite 8′ may be appliedto a mould cavity 90 in the form of a casting matrix or mould 91 withthe aid of an overpressure exerted by a plunger 92, so that the surface8 a of the carrier element will be made flat by the surface section 91 aof the mould 91.

[0185] This flat surface 8 a can now be applied directly to the supportsurface 1 c′ of the mould half 1 c.

[0186] With regard to the thickness of the layer 7, a basic rule is thatthe thickness will be sufficient to prevent a collapse or crackformation occurring during a chosen number of casting or mouldingprocesses. This means, in practice, a thickness of 1-5 μm.

[0187] More generally, the thickness may range between 1 and 50 μm, andwill preferably be less than 20 μm.

[0188] In certain applications, however, the layer may have a thinnessof about 0.1 μm, depending on the material from which the carrierelement 8 is formed, among other things.

[0189] The thickness of the wear layer 9 may be between 1 and 50 μm,preferably less than 20 μm.

[0190] The depth variation of the microstructure 1 a may vary between0.1 and 1000 μm, and will preferably be above 100 μm. in a furtherembodiment of the present invention, the matrix 2 is provided with meansfor improving the replication of its microstructure 2 a on the plasticelement 3. As mentioned above, the matrix 2 in a known way is providedon one surface with a layer 7 having a negative surface structure 2 aand against which negative surface structure 2 a a positive surfacestructure 3 a belonging to a plastic element 3 is formed.

[0191] The manufacturing of the plastic element 3 occurs principallythrough the mould half 1 c and 1 d taking up a joined together positionand thereby forming said mould cavity 1 e.

[0192] Before the moulding sequence, the mould halves 1 c and 1 d areheated in order to facilitate the distribution and the filling of themould cavity I e by a heated plastic mass (approximately 400° C.).

[0193] Normally the mould halves 1 c and 1 d and the matrix 2 are givena considerably lower temperature than the plastic mass and there is arisk that a hot (say approximately 400° C.) plastic mass does not manageto fill the mould cavity le and flow out to the edges before the plasticmass solidifies against the surface 2 a of the matrix 2. Subsequentlythe plastic mass is cooled so that at least the surface structure 3 a ofthe plastic element is solid (say approximately 140° C.) and then themould halves 1 c and 1 d are opened and the plastic element ejected (inaccordance with FIG. 3). In practice, the method requires a rapidtemperature change and the cycle times for the manufacture of plasticelements 3 are strongly dependent on the speed and the efficiency ofthis temperature changing.

[0194] The present invention is based upon that a required heating shalltake place in the surface structure belonging to the layer 7 of thematrix 2 or in a layer situated close to this layer and especially thatthe necessary heating should be able to be concentrated to the partswhere a risk for a incomplete filling is specially imminent withincreased production speed.

[0195] The invention now suggests that the used mould halves 1 c and 1d, and also a part of the matrix 2, shall through having a more or lessconstant application of cooling means be given a comparatively lowtemperature in order to be present as an available cooling capacityimmediately after the end of a moulding process. The lower that thistemperature is, the quicker the cooling, but in practice a temperatureof 80° C. is preferable with a plastic solidification temperature of140° C. In practice, a suitable temperature difference between thesolidifying temperature of the plastic material and the temperature ofthe mould halves should be between 40-100° C., such as approximately50-70° C., in an application in accordance with the present invention

[0196] The whole of the layer 7 of the matrix 2 or in any case one ormore local parts thereof shall be preheated via an electrical productionof heat to a suitable moulding temperature immediately before thecommencement of the moulding process.

[0197] In practice, it is so that the layer 7 is heated up by the hotplastic mass when this plastic mass is injected into the mould cavity.In the region around the cavity inlet 1 f, the region 21 a, the injectedplastic mass 1 p will keep the layer 7 hot so that a complete fillingwill take place despite the cooling effect of the matrix layer 7. Formore peripheral surface sections, such as the region 21 b, the injectedplastic mass 1 p will have been cooled down by the layer 7 and it iswithin this region that a incomplete filling occurs because of anextremely thin plastic layer, a skin layer, solidifying against thelayer 7 of the matrix 2 It is in order to eliminate the occurrence ofsuch skin layers 1 s that the present invention relates to a localheating of the layer 7 of the matrix 2 in at least the region 21 b.

[0198] The layer 21 b of the matrix normally does not need to have avery high temperature from the local heating and a temperature around orsomething over the actual solidification temperature is normallysufficient. The invention can however offer a temperature for the region21 b of the layer 7 which can be up to an extremely high temperature,say over 200° C.

[0199] The arrangement belonging to the matrix in accordance with theinvention, is further based upon the use of a heating means 4, in orderto, in the first instance, for a short duration of time, supply saidmatrix 2 and/or the selected region (21 b) with a requisite heat energy

[0200] The necessary cooling can take place through keeping the mouldhalves 1 c and 1 d constantly cold via a (not shown) cooling means.

[0201] The invention can be considered such that immediately before, andpreferably during, the moulding process the electrical heat energyshould be supplied to form a thin heat layer between the matrix surface2 a and the mould half 1 c in order to facilitate good filling of themould by the hot plastic mass.

[0202] When the electrical heat energy is disconnected the matrixsurface 2 a and the layer 7 are quickly cooled down to a temperaturebelow the solidifying point for the plastic mass through the lowtemperature which is being selected to be in force on the mould halvesrising up through the layer 7 and the hot plastic element 3 present inthe mould cavity 1 e In this way, the cycle time for the manufacture ofeach such plastic element 3 is reduced

[0203]FIG. 10 shows that the one connection wire 4 a of the heatingmeans 4 is connected to the outer peripheral edge 2 b of the matrix 2and the other connection 4 b is connected to the central edge 2 c of thematrix as connection points 2 b′ respectively 2 c′ It is assumed thatthese connection points 2 b′ and 2 c′ are connected to the layer 7 whichcan be electrically conducting or to one or more underlying layers suchas 31, 41, 42 and 52 which can be electrically conducting orsemi-conducting.

[0204] With reference to the FIGS. 11-14 the present invention'sspecific characteristics will now be closely illustrated throughdescribing a number of different materials and constructions for thenegative surface structure 2 a of the matrix 2 and the layer 7 with theadjacent underlying layers

[0205] The following description comprises for the sake of simplicityonly the layer 7 and a number of layers belonging to the matrix situatedclose to this layer.

[0206] Heating means 4 referred to in accordance with the invention isthe supply of electrical heat energy to the whole or selected parts ofthe matrix 2 and directly or indirectly to the layer 7, and via aswitching means (not shown) heat energy is supplied immediately beforeand during the injection moulding process in order to keep the walls ofthe matrix hot and thereby facilitate that the hot plastic mass flowsout

[0207] The connection shown in FIG. 10 for manufacturing a circular disk3 (e.g. a compact disc) implies a higher current density and a higherheat emission from the surface part 21 a of the layer 7 adjacent thecentral edge of the hole 2 c than within the peripheral edge 2 b and thesurface region 21 b.

[0208] This condition actually counteracts the primary necessity since afurther heating of the surface part 21 a can hardly be considerednecessary

[0209] Heating up of the part of the surface 21 b is on the other handnecessary A first possibility for this is offered by overheating thesurface section 21 a in the aid of an adapted heat supply to the surfacesection 21 b when layer 7 is essentially evenly thick.

[0210] Another possibility is to allocate different thicknesses to thelayer 7 with a thinner layer across the direction of current in thesurface section 21 b than in the surface section 21 a and with a thereofguaranteed increased heat development in the surface section 21 b

[0211] Preferably said electrical heat energy is applied via orimmediately next to the layer 7 of the negative surface structure 2 abelonging to the matrix and FIG. 11 illustrates an embodiment where theelectrical heat energy can be supplied only via the thin layer 7 of thesurface structure 2 a.

[0212] The optimal thickness of the layer 7 depends on the selectedmanufacturing process, selected plastic material, design of the matrix,selected concentrated heat production within the selected partialregions and many other criteria Practical experience shows that in manyapplications the thickness should be selected to be less than 20 μm, say2-10 μm, or up to 5 μm.

[0213] With the electrical connections shown in FIG. 11, if layer 7 ismade of just one type of material then more heat will produced in thecentral part 2 c while a lesser energy production will occur in theperipheral part 2 b due to the differing current densities. Such anembodiment should possibly be especially suitable if the microstructurearound the central edge 3 c in the element 3 is sensitive to themoulding conditions and, therefore, in order to obtain a goodreplication capacity and mould filling, a higher temperature of theplastic mass and the matrix is required there than in the peripheralregion.

[0214] A suitable precondition for the present invention is furthermore,according to FIG. 11, that said layer 7 having the negative surfacestructure 2 a and/or a layer 31 supporting this layer 7 consist(s) of anelectrically conducting or electrically semi-conducting, material Whenconnected in accordance with FIG. 10 the connection points 2 b′ and 2 c′can be connected to just layer 7, just layer 31 or to both layers 7 and31. The layer 31 can consist of an electrically conducting polymer. Thelayer 7 having the negative surface structure belonging to the matrix ispreferably made of a material, such as nickel, with a resistivity ofbetween 0.025 and 0.12 Ohms×mm²/m.

[0215] The local heat production across the direction of the currentflow can be regulated through locally changing the thickness (andconsequently the cross-sectional area) of the layer 7, with a thinnerlayer of material where a higher heat production is required and athicker layer of material where a lower heat production is required.Regard should paid to the current density occurring in the material toprevent it being damaged.

[0216] Said layer 7 having the negative surface structure belonging tothe matrix is, in FIG. 12, supported by a layer 41 with a resistivity of0.03 Ohms×mm²/m or less The thickness of the layer 41 should be selecteddepending on the relevant criteria, in the same way as for the layer 7.Practical experience shows that in many applications the thicknessshould be selected to be less than 20 μm, preferably thinner than 100 μmand advantageously up to 5 μm. The layer 41 can advantageously be madeof gold, silver or the like.

[0217] A further supporting layer 42 can be formed of a heat producingand/or supporting layer, where said supporting layer 42 can consist of amaterial with high resistivity. An electrically conducting polymer canalso be used here FIG. 13 shows a layer 52 having a high resistivityintermediately positioned between two thin layers 41, 51 that each havea low resistivity FIG. 13 also shows that the layer 7 can be the same asthe layer 7 according to FIG. 11, that the layer 41 can be the same asthe layer 41 in FIG. 4 and that a supporting layer 42 can be formed fromthe further supporting layer 52. It is especially advantageous that thelayer 52 can have different thicknesses (i.e. varying cross-sectionalareas), thicker at sections which require low heat energy and thinner atsections which require higher heat energy. In this embodiment, thevoltage from the heating means 4 is connected to layers 41 and 51

[0218] The invention has a special application where the layer 7 havingthe negative surface structure 2 a belonging to the matrix has the formof a microstructure 2 a and this microstructure 2 a is to be transferredto the plastic element 3 as a positive micro-related surface structure 3a. In this application it is especially important to allow the heatproduction to be adapted to be higher at some selected surface sectionsbelonging to the matrix than at other surface sections in order tothereby increase the replication accuracy and degree of mould filling ormould filling capacity.

[0219]FIG. 14 shows a further embodiment of the present invention. Thepractical application here also requires dimensional variations withinwide ranges The thickness of the layer 7 should be selected to be lessthan 10 μm, say 2-8 μm. As an example, the layer 7 here consists of anup to 5 μum thick titanium nitride which gives a hard surface 21 arespectively 21 b against the plastic element 3 and has good wear- andrelease characteristics. The layer 41 can consist of an up to 300 μmthick nickel layer that gives a hard coating and forms a support andcarrier for the layer 7 Nickel is relatively cheap and can be consideredto have acceptable electrical conductivity The layer 61 should consistof a material with good electrical characteristics such as gold, silver,copper The thickness of this layer should be thin, say less than 10 μm,for example 2-8 μm and preferably under 5 μm. The supporting layer 62can be made of a polymer material which can be plated and which acts asa heat shield. These layers can be applied advantageously with knowntechniques such as surface deposition, plating, casting, spinning, spraypainting or via vacuum deposition techniques such as sputtering orvaporisation.

[0220] It will be understood that the invention is not restricted to thepresent described and illustrated exemplifying embodiments thereof andthat modifications can be made in accordance with the concept of theinvention as defined in the accompanying claims. Furthermore, featuresshown in the individual embodiments described above may be combined withfeatures from other embodiments, thus, for example, the heating means ofthe present invention may be combined with any suitable layers andcarrier elements of the present invention.

1. A method of producing a matrix, for use in plastic element-producingmachine, wherein said matrix has a negative microstructure on onesurface, and wherein said matrix can be produced by coating with a layerof material a master that has a positive microstructure on one sidesurface thereof, characterized by the steps of: applying to saidpositive microstructure on said one side surface of said master a thinwear-resistant layer that serves as a first wear surface, wherein saidlayer presents irregularities that correspond essentially to saidmicrostructure; and filling said irregularities with a plastic compositeto form a carrier element 2 A method according to claim 1, characterizedby the step of applying said plastic composite in a mould cavity
 3. Amethod according to claims 1 and 2, characterized by the step ofselecting the plastic composite from a mixture of polymeric material andfilling material, such as quartz-filled or metal-filled epoxy orsilicone polymer, or a bicomponent composite
 4. A method according toany of claims 1-3, characterized by the step of selecting the plasticcomposite and the resultant carrier element to have a coefficient oflinear expansion and/or a thermal conductivity and/or a heat capacitythat is/are adapted for a given process in the moulding machine.
 5. Amethod according to any of claims 1-4, characterized by the step ofcuring (hardeningd) the plastic composite by applying heat and/or byirradiating with UV-light.
 6. A method according to any of claims 1-5,characterized by the step of selecting a plastic composite beneath ahard first wear layer to have an adapted thermal conductivity and/orheat capacity such as to maintain the plastic mass pressed into amachine in a hot state.
 7. A method according to any of claims 1-6,characterized by the step of coating the matrix with a second wear layeron the surface thereof distal from said first wear layer. 8 A methodaccording to any of claims 1-7, characterized by the step of making saidfirst wear layer and/or said second wear layer from titanium nitride ordiamond-like-carbon (DLC).
 9. A method according to any of claims 1-8,characterized by the steps of making said first wear layer a metal layerwhich is applied by a sputtering process and/or a vapour depositionprocess, or by a metal plating or cladding process. 10 A methodaccording to any of claims 1-9, characterized by the step of makingsmooth the surface structure of the plastic composite on that surfacewhich lies distal from said first wear surface and/or metal surface. 11.A method according to any of the previous claims characterized by thestep of providing said matrix with heating means to supply heat energyto said matrix
 12. A method according to claim 11 characterized by thestep of arranging that said heating means provides a supply ofelectrical heat energy to the whole or part of the matrix; and that saidelectrical heat energy is supplied via, or immediately adjacent to, thesurface structure belonging to the matrix wherein said surface layerhaving the surface structure and/or a layer supporting this layerconsist of an electrically conducting or electrically semi-conductingmaterial. 13 A matrix adapted for use in plastic element-producingmachine such as an injection moulding press and/or embossing machine,said matrix having a surface that presents a negative microstructure,characterized in that the microstructure includes a first wear surface,such as a metal surface, that consists of a thin wear layer; and in thatthis layer is supported by a carrier surface of a carrier element.
 14. Amatrix according to claim 13, characterized in that the carrier elementis comprised of a plastic composite.
 15. A matrix according to either ofclaims 13 or 14, characterized in that the carrier element is comprisedof a plastic composite with a mixture of polymeric material and afiller, such as a quartz-filled or metal-filled epoxy or siliconepolymer, or a bicomponent plastic material. 16 A matrix according to anyof claims 13-15, characterized in that the carrier element and/or thefirst wear layer is comprised of a material that has a coefficient oflinear expansion and/or a thermal conductivity and/or a heat capacityadapted to a given process in the machine used 17 A matrix according toany of claims 13-16 characterized in that the carrier element iscomprised of a plastic composite that can be cured by applying heatand/or by irradiating with UV-light.
 18. A matrix according to any ofclaims 113-17, characterized in that the carrier element is comprisedsolely of material that has a low thermal conductivity. 19 A matrixaccording to any of claims 13-18, characterized in that the carrierelement is reinforced
 20. A matrix according to any of claims 13-19,characterized in that the carrier element is reinforced with a secondwear layer on its surface that lies distal from the first wear layer. 21A matrix according to any of claims 13-20, characterized in that saidfirst wear layer and/or said second reinforcing layer is/are comprisedof titanium nitride or diamond-like-carbon (DLC). 22 A matrix accordingto any of claims 13-21 characterized in that it is suitable formanufacturing optical discs.
 23. A matrix according to any of claims13-22 characterized in that it has heating means to supply heat energyto said matrix, wherein said means provides a supply of electrical heatenergy to the whole or part of the matrix, that said electrical heatenergy is supplied via, or immediately adjacent to, the surfacestructure belonging to the matrix and that said surface layer having thesurface structure and/or a layer supporting this layer consist of anelectrically conducting or electrically semi-conducting material. 24.Matrix according to claim 23, characterized in that the layer having thesurface structure belonging to the matrix is selected from a materialwith a resistivity of between 0.025 and 0.12 Ohms×mm²/m.
 25. Matrixaccording to either claim 23 or 24, characterized in that said layerhaving the surface structure belonging to said matrix is supported by alayer with a resistivity of 0.03 Ohms×mm²/m or less
 26. Matrix accordingto any of claims 23-25, characterized in that the supporting layercomprises a heat producing layer.
 27. Matrix according to any of claims23-26, characterized in that said supporting layer consists of amaterial with high resistivity and which supporting layer is positionedbetween two layers with low resistivity.
 28. Matrix according to any ofclaims 23-27, characterized in that said layer is selected to anon-constant thickness, being thicker at the sections which requirelower heat energy and thinner at sections which require high heatenergy.
 29. Matrix according to any of claims 23-28, characterized inthat said layer having the negative surface structure belonging to thematrix has a surface structure having the form of a microstructure. 30.Matrix according to any of claims 23-29, characterised in that theproduction of heat is adapted to at selected surface sections to behigher that other surface sections in order to thereby increase thereplication accuracy and mould filling.
 31. Matrix according to any ofclaims 23-30, characterised in that electrical heat energy is suppliedthrough applying a voltage to the surface parts of a selected layer. 32Matrix according to any of claims 23-31, characterized in that theelectrical heat energy is supplied through applying a voltage toperipheral surface parts for different layers with low resistivity andfor heat production within an layer having a high resistivity whichlayer is positioned between said different layers with low resistivity.33. Use of a matrix in accordance with any of the previous claims tomake a plastic element.
 34. Plastic element, for example an opticaldisc, made from a matrix in accordance with any of the previous claims